Profitable and competitive trawl fishing calls for the dragging of a large net behind a powerful fishing boat. The net is hauled by a complex assembly of warp lines forming the tow gear. The net must be long and narrow for efficient collection of the catch, but must sweep a large area, in terms of opening cross-section, in order to collect as many fish as possible in one pass. Since a large-mouthed net does not have a natural tendency to open widely, the mouth of the net must be spread open during a trawling pass. It is the common practice in this art to use hydrodynamic spreaders ranging in complexity from primitive, rectangular, flat wooden "otter" doors through sophisticated oval, cambered, slotted steel doors. These doors use a sideways or radially directed hydrodynamic "lift" to spread the net mouth during a trawling pass. The most effective doors tend to be heavy, awkward, devices requiring complex and expensive hauling gear; and presenting a large amount of forward resistance to the dragging vessel. The standard "V" doors of the bottom dragger tend to be unstable on rough ground. Less cumbersome new Japanese trawls, having spreading power provided by semi-rigid fabric wings on aluminum frames, appear to have a speed limitation as they are presently developed.
The doors of present trawl nets are usually designed for only one or another of the various possible trawling depths; shallow, mid-water, and bottom dragging. Changing from one type of trawling to another usually means a change of doors and other gear is the change can be made at all with equipment on hand on the particular vessel involved.
Nets with presently available doors are difficult to haul in, especially these of bottom draggers which have hung up on obstructions on the ocean floor.
These and other difficulties of the prior art nets have been obviated in a novel manner by the present invention.
It is therefore, a primary object of the present invention to provide a trawling apparatus utilizing a positive spreading net which is spread without the use of doors, thereby achieving economy by reducing water resistance as well as by reducing warp hardware and handling time.
Another major object of the present invention is to provide a trawling apparatus in which the spreading apparatus may be reversed to collapse the net for hauling in.
A further object of the present invention is to provide a trawling apparatus which may be used at a variety of trawling depths without hauling in the gear and resetting.
Another object of the invention is to provide a trawling apparatus which is equipped with a drag tension monitor and safety release.
A still further object of the invention is to provide a trawl system which is adapted to be fully monitored and controlled for largely automated operation.
Another object of the invention is to provide a trawling apparatus which is simple in construction, economical to manufacture, and capable of a long life of useful service with minimum maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.